Acidity.
The pH ( hydrogen potential ) measures the concentration of H+ ions in the water, representing the balance between acidity and alkalinity on a scale of 0 to 14, with 7 being neutral.
Classification of the water according to its pH.
It characterises a large number of physico-chemical equilibriums and depends on many factors, including the origin of the water.
It can have a direct influence on the toxicity of other elements: sulphur is present as toxic H2S under acidic conditions, but as a harmless precipitate of S2 at pH > 13.
pH also has an influence on chlorination efficiency ( best results are achieved in acidic waters, below pH7, and chemically-assisted flocculation ( aluminium sulphate is most effective between pH 6 and 8 ).
Analyses to be done in-situ with pH-meter or colorimeter.
Alkalinity.
Alkalinity corresponds to measurement of constituents from the group of weak acid anions capable of reacting with H+.
The alkalinity of water is a measure of its capacity to neutralise acids.
This parameter plays a major role in the buffer-effect of water.
It determines the way in which pH is modified by the addition of weak acids or bases, particularly during treatment processes ( flocculation and disinfection ).